lecture15 - Mars astrobiology experiments Only astrobiology...

1 Extraterrestrial Life: Spring 2008 Mars astrobiology experiments Only astrobiology experiments so far ﬂew on the NASA Viking landers in the 1970s Pair of identical orbiters and landers Survived on the surface for 4-6 years Carried cameras, chemical and biological experiments. Boom to scrape soil from the near-surface for analysis. Basic principle of all 3 biology experiments was similar: • expose soil to an environment favorable for life: (water, light, `nutrients ’ ) • wait • search for byproducts of life (CO 2 , O 2 , CH 4 ) Discriminate between life and abiological chemical reactions using a control experiment- repeat the experiments using soil that had been heated to 160C to completely sterilize any living organisms. On Earth, these experiments were shown to yield positive results for life in the standard case, and negative results for the control. Labeled release experiment Added 1 ml of nutrient (water plus organic compounds) to 0.5 cm 3 of Martian soil Organic compounds were `labeled ’ (marked) with radioactive carbon ( 14 C isotope) Sample was incubated for 10 days Gases were analyzed for 14 C On Earth, microbes would give off CO 2 , CO and CH 4 which would contain the radioactive isotope and could be detected Result: radioactive gas was rapidly released when the nutrient was added. Second addition caused an initial drop

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